1. Field of the Invention
The present invention relates to a flow through type liquid analyzer, in particular a flow through type liquid analyzer provided with a passage-change over valve mechanism for selectively supplying an analytical portion of the analyzer with various kinds of liquid supplied through a peristaltic pump and a bubble-adding mechanism for adding bubbles to the liquid sent to said analytical portion from said passage-change over mechanism.
2. Description of the Prior Art
In a liquid analyzer of this type, since it is important to supply an analytical portion of the analyzer with a sample liquid or various kinds of liquid to be measured little by little, a peristaltic pump (called also a tubing pump) has been used for the liquid-supplying means, as above described. Also, since various hindrance to the measurements, such as a disturbance of the liquid in the analytical portion, a change in the property and state of the liquids and the interference of liquids with each other, have occurred when various kinds of liquid are continuously introduced into said analytical portion, it has been the practice to use an air bubble-adding mechanism for adding air bubbles to a liquid sent to said analytical portion from a passage-change over valve mechanism when the passages of said passage-change over valve mechanism are changed over for selectively supplying the analytical portion with various kinds of liquid sent by said peristaltic pump. Close attention has been paid to the control of the frequency of rotation of said peristaltic pump to keep it at a constant value, and to highly accurate maintenance of the standards, such as the inside diameter, the outside diameter and elastic modulus, of the liquid-supplying tube used in the peristaltic pump at the appointed values in order to control the quantity of the liquid supplied to said analytical portion with high accuracy.
However, since the quantity of the liquid supplied to said analytical portion is very small, the slightest manufacturing error in the liquid-supplying tube used in said peristaltic pump, which is the liquid-supplying means, has an unnegligibly great influence upon the quantity of the liquid supplied to said analytical portion. Accordingly, not only is it very difficult to obtain liquid analyzers having identical standards to a problem-free extent, but also much waste is apt to be produced. Also, since the characteristics of the liquid-supplying tube are apt to change due to a deterioration in elasticity and a change in shape during the use thereof, the quantity of the liquid supplied by the peristaltic pump changes rather significantly with the passage of time. In addition, since such change in the quantity of liquid supplied by the peristaltic pump due to the change in the tube characteristics is very significant immediately after the start of use of the tube, this problem cannot be eliminated by simply replacing the tube. Moreover, this problem becomes a particularly big hindrance in the event that the quantity of liquid supplied is changed, i.e. the rate of operation of the pump is changed.